1. Field of the Invention
The present invention relates to in-line shift transmissions for small tractors, riding mowers, and the like. More specifically, the field of the invention is that of parking brakes for in-line transmissions.
2. Prior Art
In-line shift transmissions include a plurality of linked transmission shafts, with one of the shafts being a shift shaft supporting a plurality of rotatable spur gears. Disposed axially within the shift shaft are keys which can engage internal keyways of the spur gears and thereby rotatably connect the engaged gear to the output shaft. The key including an elongate shaft and a head portion at one end which is biased by the shaft to extend into the gear keyway, the shaft of the key comprising a resilient metal material.
An in-line transmission is disclosed in U.S. Pat. No. 4,966,574, assigned to assignee of the present invention, the disclosure of which is explicitly incorporated by reference. The housing is made of a lighter metal, such as aluminum, and rotatably supports the transmission shafts. The shifting mechanism of the '574 transmission includes a pair of axially movable shift keys disposed in longitudinal channels of the shift shaft. The shift keys rotatably couple the shift shaft with one of the spur gears. Each key has a base portion engaging a shift collar which is axially slidable on the shift shaft. The collar has a peripheral groove receiving a pin of a shift fork. The shift fork can pivot within the housing and is connected to the shifting mechanism of the vehicle.
The shift fork, pin, and annular groove permit the collar, and hence the keys, to be moved axially while the keys are at the same time rotating with the shift shaft. Each of the spur gears journalled on the shift shaft has on its inner circumference four circumferentially spaced keyways which may be engaged by the keys to rotatably couple the shift shaft with the selected spur gear. The keys have triangular key heads and flexible spring shank portions which spring bias the key heads radially outward and into the keyways.
The vehicles which include in-line shift transmissions may also include a parking brake for locking the position of the vehicle, which is in addition to the braking system used to decelerate the vehicle. Further, many such vehicles also include an additional implement that may be used when the vehicle is stationary, e.g., a chopper or shredder. The motor of the vehicle is used to drive the additional implement, causing vibration and movement which makes having a parking brake more important. However, to provide a parking brake in such a transmission, a separate parking brake mechanism is required, for example a brake disc, a pair of parking brake pads, and a mechanism for clamping the brake pads on the brake disc. Providing a separate parking brake mechanism and associated linkage requires additional materials and further assembly which increases the cost of manufacturing the transmission, and also increases the amount of linkage with the transmission which may require additional maintenance.
As an alternative to a separate parking brake mechanism, a parking brake keyway may be cast into the transmission housing so that the shift shaft cannot rotate when a key is engaged with the parking brake keyway, thus stopping the output of the transmission. However, to withstand the rotational force of the shift shaft, the housing must be made of a stronger, more durable material, such as a heavier metal like iron or steel. This requires that the transmission housing be made of a more expensive material because such durable materials generally cost significantly more than lighter metals. Further, the increased weight of the housing due to the heavier metal of the housing adding to the load on the vehicle thus impairing performance.
What is needed is a more economical transmission parking brake for small tractors, riding mowers, and the like.
Also needed is a parking brake arrangement for transmissions of vehicles having additional implements.